Linear motor

ABSTRACT

A linear motor comprises a stator including a stator yoke and a plurality of permanent magnets arranged side by side on the stator yoke along a motor running direction in alternately reversed directions to produce alternating polarities, and a moving part including a plurality of magnetic teeth arranged along the motor running direction and coils wound around the individual magnetic teeth. Cutouts formed in end surfaces of yoke portions of the individual magnetic teeth opposite to their side facing the stator line up to form a groove-shaped channel running through the yoke portions of the successive magnetic teeth, and the multiple magnetic teeth are joined together into a single structure by fitting a connecting bar in the groove-shaped channel.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a linear motor. Moreparticularly, the invention pertains to a linear motor used in a tablefeed mechanism of a machine tool.

[0003] 2. Description of the Background Art

[0004]FIG. 20 is a cross-sectional diagram showing the construction of aconventional linear motor disclosed in Japanese Laid-open PatentPublication No. 2000-217334.

[0005] Referring to FIG. 20, a stator 1 includes a plurality ofpermanent magnets 3 a, 3 b arranged in a line at regular intervals on astator yoke 2 in alternately reversed directions to produce alternatingpolarities. A moving part 4 moves along the stator 1 as if sliding overthe stator 1 with a specific distance (gap) therefrom.

[0006] The moving part 4 includes a moving yoke 5, connecting parts 7each having a trapezoidal cross section which are held at specificintervals on one side of the moving yoke 5 facing the stator 1 by bolts6 fitted in the moving yoke 5, a plurality of magnetic teeth (poles) 8generally T-shaped in cross section and joined to the individualconnecting parts 7 which are fitted into dovetail grooves 8 a formed ina central part of each tooth end, each magnetic tooth 8 having a recess8 b and a protrusion 8 c formed on opposite sides, and a plurality ofmagnetic teeth (poles) 9 generally I-shaped in cross section and fittedbetween the successive magnetic teeth 8 as a recess 9 a and a protrusion9 b formed on opposite sides of each magnetic tooth 9 fit over and intothe protrusion 8 c and the recess 8 b of the adjoining magnetic teeth 8,respectively. Also included in the moving part 4 are coils 10individually wound around the magnetic teeth 8, 9 and a resin molding 11surrounding the magnetic teeth 8, 9 and the coils 10 to join themtogether into a single structure.

[0007] In the conventional linear motor thus constructed, the movingpart 4 is assembled by first winding the coils 10 around the individualmagnetic teeth 8, 9. Next, the dovetail grooves 8 a formed in theindividual magnetic teeth 8 are fitted over the respective connectingparts 7 held by the bolts 6 fitted in the moving yoke 5 by sliding themagnetic teeth 8 in a direction perpendicular to the plane of the paper(FIG. 20) and, when the magnetic teeth 8 have been set into position,they are fixed to the moving yoke 5 by tightening the bolts 6. Then, theindividual magnetic teeth 9 are slid between the successive magneticteeth 8 with the recess 9 a and the protrusion 9 b formed on eachmagnetic tooth 9 meshed with the protrusion 8 c and the recess 8 b ofthe adjoining magnetic teeth 8, respectively. Finally, the alternatelyarranged magnetic teeth 8, 9 and the coils 10 are joined together into asingle structure by the resin molding 11.

[0008] Since the conventional linear motor is assembled by inserting themagnetic teeth 9 between the successive magnetic teeth 8 as statedabove, the coils 10 wound around the magnetic teeth 9 slide over thecoils 10 wound around the magnetic teeth 8 with friction. This assemblyprocess could cause damages to the coils 10, such as an insulationfailure or a wire breakage, resulting in a reduction in reliability.

[0009] Furthermore, the conventional linear motor is associated with apoor labor efficiency problem. This is because its assembly involvesrather complicated procedures including fitting and sliding the dovetailgrooves 8 a formed in the individual magnetic teeth 8 over therespective connecting parts 7, tightening the bolts 6 to fix themagnetic teeth 8 to the moving yoke 5, mating the recess 9 a and theprotrusion 9 b formed on each magnetic tooth 9 with the protrusion 8 cand the recess 8 b of the adjoining magnetic teeth 8 and sliding them tofit the magnetic teeth 9 between the successive magnetic teeth 8.

[0010] Generally, magnetic teeth are manufactured by stacking press-cutelectromagnetic steel sheets. Accordingly, the stacking thickness of theelectromagnetic steel sheets should be increased if it is necessary toincrease the width of the individual magnetic teeth due to an increasein motor capacity. An increase in the stacking thickness tends to causean inclination of the stacked electromagnetic steel sheets due tostacking errors as well as a deterioration in assembling efficiency. Inaddition, it is necessary to increase the thickness of a lower press dieif the stacking thickness increases. This would lead to an increase incost for making the die and an eventual rise in manufacturing cost ofthe magnetic teeth.

[0011] Even when the structure of magnetic teeth does not adopt theaforementioned steel sheet stacking design, it is still necessary tovary the width of the individual magnetic teeth with changes in motorcapacity, and this makes it difficult to attain desirable levels ofefficiency with respect to the control of production and inventory ofvarious components.

SUMMARY OF THE INVENTION

[0012] In light of the aforementioned problems of the prior art, it isan object of the invention to provide a novel structure for joining aplurality of magnetic teeth into a single structure. More specifically,it is an object of the invention to provide a linear motor adopting amagnetic tooth joining structure which permits improvements inreliability of a magnetic tooth assembly and in assembling efficiency.It is also an object of the invention to enable a cost reduction byimproving the efficiency of controlling the production and inventory ofcomponents regardless of changes in motor capacity.

[0013] According to a principal feature of the invention, a linear motorcomprises a stator including a stator yoke extending in a motor runningdirection and a plurality of permanent magnets arranged on the statoryoke at regular intervals along the motor running direction inalternately reversed directions to produce alternating polarities, and amoving part positioned generally parallel to the permanent magnets ofthe stator and separated therefrom by a specific gap, the moving partincluding a plurality of magnetic teeth arranged side by side along themotor running direction and coils wound around the individual magneticteeth. In this linear motor, each of the magnetic teeth has a yokeportion located opposite to a side facing the stator, the yoke portionof each magnetic tooth being held in contact with the yoke portion ofeach adjoining magnetic tooth, and a tooth portion around which the coilis wound, the tooth portion extending from the yoke portion toward thestator. Cutouts formed in end surfaces of the yoke portions of theindividual magnetic teeth opposite to their side facing the stator lineup to form a groove-shaped channel running through the yoke portions ofthe successive magnetic teeth, and the multiple magnetic teeth arejoined together into a single structure by fitting a connecting memberin the groove-shaped channel.

[0014] The linear motor thus constructed offers enhanced reliability andgreater assembling efficiency.

[0015] These and other objects, features and advantages of the inventionwill become more apparent upon reading the following detaileddescription along with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIGS. 1A-1B are diagrams showing the construction of a linearmotor according to a first embodiment of the invention, in which FIG. 1Ais a plan view and FIG. 1B is a cross-sectional side view;

[0017]FIG. 2 is a front view of the linear motor of FIGS. 1A-1B;

[0018]FIG. 3 is a plan view showing how magnetic teeth of the linearmotor are successively arranged;

[0019]FIG. 4 is a front view showing how the magnetic teeth are joinedinto a single structure by means of connecting bars;

[0020]FIG. 5 is a front view showing how the connecting bars are weldedto the magnetic teeth;

[0021]FIG. 6 is a plan view showing an assembly of the magnetic teethupon completion of a welding process shown in FIG. 5;

[0022]FIG. 7 is a diagram showing details of how each connecting bar iswelded to the magnetic teeth;

[0023]FIG. 8 is a plan view showing the construction of a linear motoraccording to a second embodiment of the invention;

[0024]FIG. 9 is a front view of the linear motor of FIG. 8;

[0025]FIG. 10 is a perspective view showing a process of winding a coilaround one of magnetic teeth shown in FIG. 8;

[0026]FIG. 11 is a plan view showing the construction of a linear motoraccording to a third embodiment of the invention;

[0027]FIG. 12 is a side view of the linear motor of FIG. 11;

[0028]FIG. 13 is a front view of the linear motor of FIG. 11;

[0029] FIGS. 14A-14B are front views showing how connecting bars arewelded to individual magnetic teeth shown in FIG. 11;

[0030]FIG. 15 is a plan view showing an assembly of the magnetic teethupon completion of a welding process shown in FIG. 14.

[0031]FIG. 16 is a plan view showing the construction of a linear motoraccording to a fourth embodiment of the invention;

[0032]FIG. 17 is a front view showing the construction of a linear motoraccording to a fifth embodiment of the invention;

[0033]FIG. 18 is a diagram showing the relationship between thedimensions of connecting bars and groove-shaped channels;

[0034]FIG. 19 is a front view showing how the connecting bars are weldedto magnetic teeth; and

[0035]FIG. 20 is a cross-sectional diagram showing the construction of aconventional linear motor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Preferred embodiments of the invention are now described withreference to the appended drawings.

[0037] First Embodiment

[0038] FIGS. 1A-1B are diagrams showing the construction of a linearmotor according to a first embodiment of the invention, in which FIG. 1Ais a plan view and FIG. 1B is a cross-sectional side view. FIG. 2 is afront view of the linear motor of FIGS. 1A-1B, FIG. 3 is a plan viewshowing how magnetic teeth 25 of the linear motor are successivelyarranged, FIG. 4 is a front view showing how the magnetic teeth 25 arejoined into a single structure by means of connecting bars 27, FIG. 5 isa front view showing how the connecting bars 27 are welded to themagnetic teeth 25, FIG. 6 is a plan view showing an assembly of themagnetic teeth 25 upon completion of a welding process shown in FIG. 5,and FIG. 7 is a diagram showing details of how each connecting bar 27 iswelded to the magnetic teeth 25.

[0039] Referring to these Figures, a stator 21 includes a platelikestator yoke 22 extending in a motor running direction shown by doublearrows (FIGS. 1A-1B) and a plurality of permanent magnets 23, 24arranged on the stator yoke 22 at regular intervals along the motorrunning direction in alternately reversed directions to producealternating polarities. Separated by a specific distance from thepermanent magnets 23, 24 arranged on the stator yoke 22, a moving part29 includes the aforementioned multiple magnetic teeth 25 arranged alongthe motor running direction, coils 28 individually wound around themagnetic teeth 25 and the aforementioned connecting bars 27 joiningtogether the magnetic teeth 25 into a single structure.

[0040] As illustrated in FIG. 1B, upper parts of the individual magneticteeth 25 (that are opposite to ends of the magnetic teeth 25 facing thestator 21) constitute yoke portions 25 c, from which tooth portions 25 dextend downward toward the stator 21. The coils 28 are wound around theindividual tooth portions 25 d and the multiple magnetic teeth 25 arearranged side by side with side faces of their yoke portions 25 c heldin contact with one another.

[0041] Referring now to FIG. 2, a pair of cutouts 25 a (width W1, depthH2) having a rectangular cross section are formed at specific locationsin an upper end surface of the yoke portion 25 c of each magnetic tooth25 in such a manner that the cutouts 25 a in the successive yokeportions 25 c line up along the motor running direction (which isperpendicular to the plane of the paper in FIG. 2). At both uppercorners (left and right as illustrated in FIG. 2) of the yoke portion 25c of each magnetic tooth 25, there are formed cutouts 25 b each having awidth equal to one half the width W1 of each cutout 25 a (i.e., W1/2).When the magnetic teeth 25 are assembled, the cutouts 25 a formed in theindividual yoke portions 25 c line up in double straight lines andtogether form a pair of groove-shaped channels 26 running through thesuccessive magnetic teeth 25 (refer to FIGS. 1A-1B).

[0042] The aforementioned connecting bars 27 are fitted in theindividual groove-shaped channels 26 all the way along their length tojoin together the magnetic teeth 25. There are formed screw holes 27 ain the connecting bars 27 at specific positions for fixing them to anunillustrated driven part.

[0043] Assembly processes of the moving part 29 of the linear motor ofthe first embodiment thus constructed are specifically described belowreferring to the drawings.

[0044] First, the coils 28 are wound around the individual magneticteeth 25. The individual magnetic teeth 25 are then aligned with theside faces of the yoke portions 25 c placed in contact with one anotheras shown in FIG. 3. As a result, the cutouts 25 a in the individual yokeportions 25 c line up in double straight lines, together forming the twogroove-shaped channels 26. Then, the connecting bars 27 are fitted inthe groove-shaped channels 26 as shown in FIG. 4 and welded as shown inFIG. 5, so that the connecting bars 27 are firmly fixed to the yokeportions 25 c of the individual magnetic teeth 25 as shown in FIG. 6.The magnetic teeth 25 are joined together by the connecting bars 27 intoa single structure, whereby assembly of the moving part 29 is completed.

[0045] The aforementioned welding process is explained in further detailreferring to FIG. 7. What is important in this welding process is therelationship between the height H1 of the connecting bars 27 and thedepth H2 of the groove-shaped channels 26 (cutouts 25 a) as can berecognized from FIG. 7. If either of the connecting bars 27 warps due tothermal shrinkage occurring at welding points P, there arises a problemthat an array of the magnetic teeth 25 joined by the connecting bars 27,particularly a bottom surface of the moving part 29 facing the stator21, would become deformed.

[0046] It is therefore desirable that the depth H2 of the groove-shapedchannels 26 be made slightly smaller than half the height H1 of theconnecting bars 27 (i.e., H1/2) so that the welding points P are locatedgenerally at the middle of the height H1 of the connecting bars 27.

[0047] It will be recognized that if there is established a relationshipH2<H1/2, the welding points P might be located slightly below the middleof the height H1 of the connecting bars 27 depending on performance ofwelding operation. In this case, the connecting bars 27 tend to warp,swelling upward at central parts, as a result of the welding operation.Even if this situation occurs, however, deformation of the bottomsurface of the moving part 29 facing the stator 21 is made sufficientlysmall as compared to a case where the welding points P are located abovethe middle of the height H1 of the connecting bars 27. This is becauseside surfaces of the successive magnetic teeth 25 joined by theconnecting bars 27 are in direct contact with one another in theabove-described structure of the first embodiment.

[0048] As can be seen from the foregoing discussion, the cutouts 25 aformed in the upper end surfaces of the yoke portions 25 c of theindividual magnetic teeth 25 line up in double straight lines, togetherforming the two groove-shaped channels 26, and the connecting bars 27are fitted into these groove-shaped channels 26 to join together themagnetic teeth 25 into a single structure in the aforementioned firstembodiment. This structure of the embodiment facilitates assembly of themoving part 29 and helps improve assembling efficiency. In addition, theindividual magnetic teeth 25 can be assembled without causing theadjacent coils 28 to slide over each other with friction, and thisserves to prevent insulation failures and wire breakage and improvereliability.

[0049] Furthermore, it is possible to prevent warpage of the connectingbars 27 or reduce the influence of their warpage by making the depth H2of the groove-shaped channels 26 smaller than half the height H1 of theconnecting bars 27 (H2<H1/2) when fixing the connecting bars 27 into thegroove-shaped channels 26 by welding. This makes it unnecessary to carryout operation for removing the effect of warpage of the connecting bars27 and thereby improve assembling efficiency.

[0050] Second Embodiment

[0051]FIG. 8 is a plan view showing the construction of a linear motoraccording to a second embodiment of the invention, FIG. 9 is a frontview of the linear motor of FIG. 8, and FIG. 10 is a perspective viewshowing a process of winding a coil 33 around one of magnetic teeth 25shown in FIG. 8. In these Figures, elements identical to those of theforegoing first embodiment are designated by the same reference numeralsand a description of such elements is omitted.

[0052] Referring to the Figures, a stator 31 includes a stator yoke 22and permanent magnets 23 and 24 alternately arranged in a double row onthe stator yoke 22. Each of the magnetic teeth 25 constituting a movingpart 37 is formed of a pair of magnetic tooth elements 32 aligned in adirection perpendicular to a motor running direction. As depicted inFIG. 10, each pair of magnetic tooth elements 32 is held by awire-winding jig 34 and turned in a direction shown by an arrow, wherebythe two magnetic tooth elements 32 are securely joined together by thecoil 33 form by a magnet wire 35 wound around them.

[0053] In this embodiment, a plurality of magnetic teeth 25 individuallywould by the coils 33 as described above are arranged side by side withside faces of their yoke portions 25 c held in contact with one anotherin the same manner as in the first embodiment. When the magnetic teeth25 are arranged in this fashion, cutouts 25 a formed in the individualmagnetic teeth 25 line up and together form four parallel groove-shapedchannels 26 in a top surface of the moving part 37, and cutouts 25 bformed at both upper corners of the individual magnetic tooth elements32 also line up and together form a groove-shaped channel 36 bridgingthe inside upper corners of the double rows of the magnetic toothelements 32. Three connecting bars 27 are then fitted in the individualgroove-shaped channels 26, 36 as shown in FIG. 9 and fixed therein bywelding them at specific points as shown in FIG. 8. Consequently, theindividual magnetic teeth 25 are securely joined together by theconnecting bars 27 into a single structure, whereby assembly of themoving part 37 is completed.

[0054] As seen above, each magnetic tooth 25 is formed by winding thecoil 33 around a pair of magnetic tooth elements 32 arranged in tandemin a direction perpendicular to the motor running direction in theaforementioned second embodiment. This structure of the embodiment makesit possible to flexibly increase (or decrease) in accordance withchanges in required power of the linear motor (motor capacity) by acombination of the magnetic tooth elements 32. The embodiment not onlyserves to improve assembling efficiency but enables the use of the samecomponents for different purposes, facilitates the control of inventoryof various components and helps achieve an eventual cost reduction.

[0055] Particularly when the magnetic teeth are formed by stackingelectromagnetic steel sheets, they can be produced by combining themagnetic tooth elements 32 having a standardized shape and dimensions.Consequently, even when the required motor capacity increases, thestacking thickness of the electromagnetic steel sheets can be heldwithin specific limits. This serves to reduce the cost of a press die,decrease an inclination of the stacked electromagnetic steel sheets dueto stacking errors and improve productivity. If multiple magnetic toothelements 32 are stacked while reversing their directions as necessary,it would be possible to further decrease the inclination of the entireassembly of the magnetic teeth 25.

[0056] Furthermore, since the groove-shaped channel 36 formed in the topsurface of the moving part 37 bridges the double rows of the magnetictooth elements 32 and the connecting bar 27 is fitted in thegroove-shaped channel 36, the magnetic tooth elements 32 are joined evenmore securely, this serves to further improve the reliability.

[0057] While the magnetic tooth 25 of the second embodiment is formed byarranging two magnetic tooth elements 32 in tandem in a directionperpendicular to the motor running direction and uniting them by windingthe coil 33, the number of magnetic tooth elements 32 to be united intoa single structure is not necessarily limited to two, but three or moremagnetic tooth elements 32 may be jointed together to form a largermagnetic tooth.

[0058] The aforementioned method of forming a magnetic tooth byarranging multiple magnetic tooth elements in tandem in a directionperpendicular to the motor running direction and uniting them into asingle structure by a coil wound around them is not necessarily limitedto the linear motor described above employing a structure in which the aplurality of magnetic teeth 25 are joined together by the connectingbars 27. The novel method of the present embodiment can also be appliedto other structures of linear motors, such as the earlier-mentionedconventional linear motor in which the moving yoke 5 and the magneticteeth 8, 9 are separately produced and joined together by a dovetailjoint structure, facilitating the control of inventory of components andenabling a cost reduction. In a case where the magnetic teeth are formedby stacking electromagnetic steel sheets, the aforementioned method ofthe present embodiment serves to reduce the inclination of the stackedelectromagnetic steel sheets due to stacking errors, improveproductivity and reduce the cost of the press die.

[0059] Third Embodiment

[0060]FIG. 11 is a plan view showing the construction of a linear motoraccording to a third embodiment of the invention, FIG. 12 is a side viewof the linear motor of FIG. 11, FIG. 13 is a front view of the linearmotor of FIG. 11, FIGS. 14A-14B are front views showing how connectingbars 27 are welded to individual magnetic teeth 41 shown in FIG. 11, andFIG. 15 is a plan view showing an assembly of the magnetic teeth 41 uponcompletion of a welding process shown in FIG. 14. In these Figures,elements identical to those of the foregoing second embodiment aredesignated by the same reference numerals and a description of suchelements is omitted.

[0061] Referring to the Figures, each of the magnetic teeth 41constituting a moving part 42 is formed of a pair of magnetic toothelements 43 aligned in a direction perpendicular to a motor runningdirection. As described with reference to the aforementioned secondembodiment, two magnetic tooth elements 43 are fastened and joinedtogether into a single structure by a coil 33 wound around them. Asshown in FIG. 13, two projecting parts 41 b, 41 c are formed on an upperend surface of a yoke portion 41 a of each magnetic tooth element 43,the two projecting parts 41 b, 41 c being separated by a distance Wwhich is equal to the width of each connecting bar 27. There is formedanother projecting part 41 d on the upper end surface of the yokeportion 41 a of each magnetic tooth element 43. This projecting part 41d is located such that when two magnetic tooth elements 43 are alignedto form one magnetic tooth 41, the projecting parts 41 d of the magnetictooth elements 43 face each other with their facing side surfacespositioned half the width W of the connecting bar 27 (W/2) apart from aside face of each yoke portion 41 a, creating an interval W between thefacing side surfaces of the two projecting parts 41 d. Opposite sidesurfaces of the projecting parts 41 d are separated from the projectingparts 41 c of the respective magnetic tooth elements 43 by a distanceequal to W.

[0062] Assembly processes of the moving part 42 of the linear motor ofthe third embodiment thus constructed are specifically described belowreferring to the drawings.

[0063] A pair of magnetic tooth elements 43 are arranged in tandem withtheir sides held in contact with each other in such a manner that theprojecting parts 41 d formed on their yoke portions 41 a face each otherand, then, the coil 33 is wound around the two magnetic tooth elements43 to securely join them into a single structure, thereby forming eachmagnetic tooth 41. The individual magnetic teeth 41 thus formed arearranged side by side along the motor running direction with the sidefaces of their yoke portions 41 a held in contact with one another. Whenthe magnetic teeth 41 are arranged in this fashion, there are formedparallel groovelike channels 44 due to the intervals W between theprojecting parts 41 b and 41 c. There is also formed another groovelikechannel 44 between the projecting parts 41 d formed close to inner endsof the magnetic teeth 41. Then, three connecting bars 27 are fitted inthe groovelike channels 44 formed between the projecting parts 41 b and41 c and between the projecting parts 41 d as shown in FIG. 13. Theconnecting bars 27 are welded to the respective groovelike channels 44as shown in FIGS. 14A-14B, whereby upper parts of side surfaces of theconnecting bars 27 are fixed to upper edges of the individual projectingparts 41 b, 41 c, 41 d and lower parts of the side surfaces of theconnecting bars 27 are fixed to upper ends of the yoke portions 41 a. Asa result of this welding operation, the individual magnetic teeth 41aligned as described above are securely joined together by theconnecting bars 27 into a single structure, whereby assembly of themoving part 42 is completed.

[0064] As depicted in the foregoing discussion, the magnetic teeth 41are joined into a single structure by fitting and fixing the connectingbars 27 between the projecting parts 41 b and 41 c formed on the upperend surfaces of the yoke portions 41 a of the individual magnetic teeth41 and between the facing projecting parts 41 d in the third embodiment.This structure makes it possible to assemble the moving part 42 withleast effort and thereby improve assembling efficiency. In addition, themagnetic teeth 41 can be assembled without causing the adjacent coils 33to slide over each other with friction, and this serves to preventinsulation failures and wire breakage and improve reliability.

[0065] The connecting bar 27 in the middle bridges the two magnetictooth elements 43 of each magnetic tooth 41 when fitted in thegroovelike channel 44 formed between the facing projecting parts 41 d ofthe individual magnetic tooth elements 43. This serves to reinforce theone-piece assembly of the magnetic teeth 41, resulting in a furtherimprovement of reliability. Furthermore, because the individualconnecting bars 27 are fitted in the groovelike channels 44 formedbetween the projecting parts 41 b and 41 c and between the projectingparts 41 d, their welding operation is quite easy, and this also servesto improve the assembling efficiency. Moreover, their welding pointshave an increased capability to withstand a moment of force appliedthereupon as both upper and lower parts of the side surfaces of theconnecting bars 27 are welded to the magnetic tooth elements 43,resulting in an even further improvement in reliability.

[0066] As is apparent from FIG. 13, there is formed a gap as wide as Wbetween the projecting parts 41 c and 41 d of each magnetic toothelement 43. Although three connecting bars 27 are fitted in thegroovelike channels 44 formed between the projecting parts 41 b and 41 cand between the projecting parts 41 d in the third embodiment describedheretofore, additional connecting bars 27 may be fitted in groovelikechannels formed between the projecting parts 41 c and 41 d when neededto further reinforce the one-piece assembly of the magnetic teeth 41.

[0067] While the magnetic tooth 41 is formed by arranging two magnetictooth elements 43 in tandem in the aforementioned third embodiment, itis needless to say that the same advantageous effect as described abovecan be achieved by fitting the connecting bars 27 in the groovelikechannels 44 formed between the projecting parts 41 b and 41 c and/orbetween the projecting parts 41 c and 41 d even when the assembly of themagnetic teeth is formed by a single row or more than two rows of themagnetic tooth elements 43.

[0068] Fourth Embodiment

[0069]FIG. 16 is a plan view showing the construction of a linear motoraccording to a fourth embodiment of the invention, in which elementsidentical to those of the foregoing third embodiment are designated bythe same reference numerals and a description of such elements isomitted.

[0070] In this embodiment, each connecting bar 51 has a width W1 largerthan the distance W between projecting parts 41 b and 41 c, and thereare formed recesses 51 a and 51 b in both side surfaces of eachconnecting bar 51 in which the projecting parts 41 b and 41 c fit,respectively.

[0071] Since the width W1 of each connecting bar 51 is made larger thanthe distance W between the projecting parts 41 b and 41 c and therecesses 51 a and 51 b in which the projecting parts 41 b and 41 c fitare formed in both side surfaces of each connecting bar 51 in thisfourth embodiment, movements of the connecting bars 51 in theirlongitudinal direction are restricted when the projecting parts 41 b and41 c are fitted in the recesses 51 a and 51 b, respectively. Thisstructure makes it possible to attach the connecting bars 51 in positionmore securely and further improve reliability.

[0072] Fifth Embodiment

[0073] A fifth embodiment of the invention provides an optimumconstruction of connecting bars applicable when individual magneticteeth are formed by stacking electromagnetic steel sheets in a directionperpendicular to a motor running direction.

[0074] Although the connecting bars 27 (51) of the foregoing embodimentshave a rectangular cross section, connecting bars 61 of the fifthembodiment each have a downward-directed ridgelike projection as shownin FIG. 17.

[0075] In this embodiment, the direction of the width of eachgroove-shaped channel 26 formed by cutouts 25 a in yoke portions 25 c ofindividual magnetic teeth 25 matches the stacking direction of theelectromagnetic steel sheets and, therefore, the width of eachgroove-shaped channel 26 could vary due to variations in the thicknessof the individual electromagnetic steel sheets and fastening force ofcoils 28 wound around the magnetic teeth 25. For this reason, there is apossibility that gaps will occur between the connecting bar 61 and thegroove-shaped channel 26, making it impossible to obtain a stablewelding effect.

[0076] To cope with this problem, each connecting bar 61 has adownward-projecting mating part 61 a (i.e., the aforementioned ridgelikeprojection) which fits in the groove-shaped channel 26 with specificgaps between them and a flange portion 61 b which comes in contact witha top surface of the yoke portions 25 c of the magnetic teeth 25 alongthe groove-shaped channel 26.

[0077] As shown in FIG. 18, width W3 of the mating part 61 a is madesmaller than width W2 of the groove-shaped channel 26. Given thisrelationship, W2>W3, gaps G are created between the mating part 61 a andthe groove-shaped channel 26 as illustrated even when certain amounts ofvariations occur in the width W2 of the groove-shaped channel 26. Inaddition, the height H3 of the mating part 61 a is made smaller than thedepth H2 of the groove-shaped channel 26 so that a gap G is createdbetween the bottom of the mating part 61 a and the bottom of thegroove-shaped channel 26.

[0078] In the aforementioned structure, a bottom surface of the flangeportion 61 b of each connecting bar 61 comes in close contact with thetop surface of the yoke portions 25 c of the magnetic teeth 25 alongeach connecting bar 61 in a reliable fashion even when certain amountsof variations occur in the width W2 of the groove-shaped channels 26.This construction makes it possible to weld each connecting bar 61 tothe corresponding groove-shaped channel 26 along their contact areas,enabling easy and stable welding operation as shown in FIG. 19. As aresult, the multiple magnetic teeth 25 can be reliably joined togetherinto a single structure by the connecting bars 61.

[0079] While the connecting bars 61 are fitted into the groove-shapedchannels 26 formed by cutouts 25 a made in the yoke portions 25 c of theindividual magnetic teeth 25 in the fifth embodiment, the aforementionedstructure of the embodiment is also applicable to the structure of theearlier-mentioned third embodiment in which the connecting bars 27 arefitted in the groovelike channels 44 formed between the adjacentprojecting parts 41 b, 41 c, 41 d, producing the same advantageouseffect as described above.

[0080] Although not stated in the foregoing description of theindividual embodiments, it is possible to enlarge magnetic paths andimprove overall performance of the linear motor by forming theconnecting bars 27, 51, 61 with magnetic material.

What is claimed is:
 1. A linear motor comprising: a stator including astator yoke extending in a motor running direction and a plurality ofpermanent magnets arranged on the stator yoke at regular intervals alongthe motor running direction in alternately reversed directions toproduce alternating polarities; and a moving part positioned generallyparallel to the permanent magnets of the stator and separated therefromby a specific gap, the moving part including a plurality of magneticteeth arranged side by side along the motor running direction and coilswound around the individual magnetic teeth; wherein each of the magneticteeth has a yoke portion located opposite to a side facing the stator,the yoke portion of each magnetic tooth being held in contact with theyoke portion of each adjoining magnetic tooth, and a tooth portionaround which the coil is wound, the tooth portion extending from theyoke portion toward the stator; and wherein cutouts formed in endsurfaces of the yoke portions of the individual magnetic teeth oppositeto their side facing the stator line up to form a groove-shaped channelrunning through the yoke portions of the successive magnetic teeth, andthe multiple magnetic teeth are joined together into a single structureby fitting a connecting member in the groove-shaped channel.
 2. A linearmotor comprising: a stator including a stator yoke extending in a motorrunning direction and a plurality of permanent magnets arranged on thestator yoke at regular intervals along the motor running direction inalternately reversed directions to produce alternating polarities; and amoving part positioned generally parallel to the permanent magnets ofthe stator and separated therefrom by a specific gap, the moving partincluding a plurality of magnetic teeth arranged side by side along themotor running direction and coils wound around the individual magneticteeth; wherein each of the magnetic teeth has a yoke portion locatedopposite to a side facing the stator, the yoke portion of each magnetictooth being held in contact with the yoke portion of each adjoiningmagnetic tooth, and a tooth portion around which the coil is wound, thetooth portion extending from the yoke portion toward the stator; andwherein a pair of projecting parts is formed on end surfaces of the yokeportions of the individual magnetic teeth opposite to their side facingthe stator, whereby gaps between the projecting parts form a groovelikechannel running through the yoke portions of the successive magneticteeth, and the multiple magnetic teeth are joined together into a singlestructure by fitting a connecting member in the groovelike channel. 3.The linear motor according to claim 2, wherein there are formed recesseswhich engage with said projecting parts in side surfaces of saidconnecting member.
 4. The linear motor according to claim 1 , whereinsaid connecting member is fixed in said channel by welding.
 5. Thelinear motor according to claim 4, wherein each of the magnetic teeth isformed by stacking magnetic sheets in a direction perpendicular to themotor running direction, and said connecting member has a mating partwhich fits in said channel leaving specific gaps between the mating partand the channel and a flange portion which comes in contact with a topsurface of the yoke portions of the magnetic teeth along the channel. 6.The linear motor according to claim 4, wherein the depth H2 of saidchannel is made smaller than one half of the height H1 of the connectingmember, establishing a relationship H2<H1/2, so that the connectingmember projects out from the channel.
 7. The linear motor according toclaim 1 , wherein each of the magnetic teeth is formed of multiplemagnetic tooth elements arranged in tandem in a direction perpendicularto the motor running direction, and each of the coils is wound aroundsaid multiple magnetic tooth elements to join them together into asingle structure.
 8. The linear motor according to claim 7, wherein saidchannel is formed in an area bridging rows of said multiple magnetictooth elements and the connecting member is fitted in the channel thusformed.
 9. The linear motor according to claim 1, wherein saidconnecting member is made of a magnetic material.
 10. A linear motorcomprising: a stator including a stator yoke extending in a motorrunning direction and a plurality of permanent magnets arranged on thestator yoke at regular intervals along the motor running direction inalternately reversed directions to produce alternating polarities; and amoving part positioned generally parallel to the permanent magnets ofthe stator and separated therefrom by a specific gap, the moving partincluding a plurality of magnetic teeth arranged side by side along themotor running direction and coils wound around the individual magneticteeth; wherein each of the magnetic teeth is formed of multiple magnetictooth elements arranged in tandem in a direction perpendicular to themotor running direction, and each of the coils is wound around saidmultiple magnetic tooth elements to join them together into a singlestructure.